Optical amplifiers that amplify optical signals, i.e. wavelength division multiplexing signals (WDM), etc., without the need to convert the optical signals to an electrical signal. EDFAs include optical fiber doped with erbium along with associated pump lasers. Distributed Raman amplifiers utilize in-line optical fiber with associated pump lasers. Existing EDFAs use a mid-stage variable optical attenuator (VOA) to achieve variable gain operation. The variable gain operation allows the EDFAs to operate with a flat gain response over the entire bandwidth over a range of gain settings. However, the useful dynamic range, where the noise figure (NF) of the amplifier does not increase significantly with the reduction in gain, is limited to about 5 dB in conventional amplifiers. In real networks, there is a large variability or spread in the span losses. This usually requires use of multiple types of EDFA modules optimized at different gain points or use of a sub-optimal EDFA module to limit the number of module types. Disadvantageously, multiple types of EDFA modules leads to increased sparing requirements, complex manufacturing, and the like. The other factors that complicate the design are that the EDFA modules may be coupled in two directions in order to reduce the footprint. Other factors such as the presence of Distributed Raman Amplifiers whose gain is dependent of fiber type and quality increase the spread in required gain values.
It would be advantageous to have an EDFA module that could account for the large variability or spread in the span loss in actual network deployments while streamlining network operations and manufacturing requirements.